1. Field of the Invention
The present invention relates generally to a packet data service, and in particular, to a method for transmitting information on a cell available for a particular packet data service to a user equipment (UE) when the cell available for the packet data service overlaps with a cell unavailable for the packet data service thereby to provide the packet data service to the UE.
2. Description of the Related Art
FIG. 1 is a diagram schematically illustrating a configuration of a general mobile communication system. Referring to FIG. 1, the mobile communication system, a Universal Mobile Telecommunications System (UMTS) mobile communication system, is comprised of a core network (CN) 100, a plurality of radio network subsystems (RNSs) 110 and 120, and a user equipment (UE) 130. Each of the RNSs 110 and 120 includes a radio network controller (RNC) 111 and 112 and a plurality of Node Bs 113-116 (i.e. base stations). For example, the RNS 110 is comprised of an RNC 111 and Node Bs 113 and 115, and the RNS 120 is comprised of an RNC 112 and Node Bs 114 and 116.
The RNCs 111 and 112 are classified into a serving RNC (SRNC), a drift RNC (DRNC) and a controlling RNC (CRNC) according to their operation. The SRNC is an RNC that manages information on each UE and controls data exchange with the CN 100. The DRNC, when data of a UE is transmitted and received to/from the SRNC via a specific RNC, is the specific RNC. The CRNC is an RNC that controls each Node B.
For example, in FIG. 1, if information on the UE 130 is managed by the RNC 111, the RNC 111 serves as an SRNC for the UE 130, and if data of the UE 130 is transmitted and received via the RNC 112 due to movement of the UE 130, the RNC 112 becomes a DRNC of the UE 130. In addition, the RNC 111 that controls the Node B 113 in communication with the UE 130 becomes a CRNC for the Node B 113.
In FIG. 1, the RNCs 111 and 112 are connected to their Node Bs 113 to 116 via Iub interfaces, and the RNC 111 is connected to the RNC 112 via an Iur interface. Although not illustrated in FIG. 1, the UE 130 is connected to a UMTS Terrestrial Radio Access Network (UTRAN) via a Uu interface.
The RNC assigns radio resource to a plurality of their Node Bs, and each of the Node Bs provides the radio resources assigned from the RNC to the UE. The radio resources are provided on a cell-by-cell basis. The radio resources provided by the Node B are radio resources for a particular cell managed by the Node B. The UE sets up a radio channel using the radio resources for the particular cell managed by the Node B, and transmits/receives data using the set radio channel. Therefore, since the UE identifies only physical channels separately formed for cells, distinguishing between the Node B and the cell is meaningless and not necessary. Herein, the terms “Node B” and “cell” are used interchangeably.
In order to support multicast/multimedia communication, there is provided Broadcast/Multicast Service in which one data source provides a particular service to a plurality of UEs. Broadcast/Multicast Service can be divided into Cell Broadcast Service (CBS) supporting a message-based service and Multimedia Broadcast/Multicast Service (MBMS) supporting real-time images and voice, still images, text data, etc.
FIG. 2 is a diagram schematically illustrating a network configuration for providing an MBMS service in a mobile communication system. Referring to FIG. 2, a Broadcast/Multicast-service center (BM-SC) 210 is a source that provides an MBMS data stream, and the BM-SC 210 schedules an MBMS data stream and delivers the scheduled MBMS data stream to a transit network (NW) 220. The transit network 220 exists between the BM-SC 210 and a serving GPRS (General Packet Radio Services) support node (SGSN) 230, and delivers the MBMS data stream provided from the BM-SC 210 to the SGSN 230. The SGSN 230 can be comprised of a gateway GPRS support node (GGSN) and an external network. The SGSN 230 receiving the MBMS data stream from the transit network 220 controls an MBMS-related service for users, or UEs, desiring to receive an MBMS service, i.e., controls an MBMS-related service such as a service for managing MBMS accounting-related data and a service for selectively transmitting MBMS data to a particular RNC 240. In addition, the SGSN 230 configures and manages an SGSN service context for an MBMS service X, and delivers the MBMS data stream to the RNC 240.
The RNC 240 controls a plurality of Node Bs, and transmits the MBMS data to a Node B where a UE requesting the MBMS service is located among its Node Bs. In addition, the RNC 240 controls a radio channel set up procedure for providing the MBMS service, and configures and manages an RNC service context for the MBMS service X using the MBMS data stream provided from the SGSN 230.
It will be assumed herein that a Node B1 (or cell 1) 260 corresponds to a cell where a UE1 261, a UE2 262 and a UE3 263 are located, and Node B2 (or cell 2) 270 corresponds to a cell where a UE4 271 and a UE5 272 are located, and one radio channel is set up between the Node B1 260 and the UEs 261 to 263 to provide the MBMS service.
Although not illustrated in FIG. 2, a home location register (HLR) is connected to the SGSN 230 and performs user authentication for the MBMS service.
A description will now be made of an operation performed between nodes supporting an MBMS service. FIG. 3 is a message flow diagram illustrating a procedure for performing an MBMS service between an RNC and a UE desiring to receive an MBMS service.
The procedure includes 4 successive processes of Announcement, Joining, Notification, and Radio Bearer (RB) Setup processes. The 4 processes will be described herein below. In the processes, an RNC provides an MBMS service to UEs requesting the MBMS service via a Node B. Although the Node B is not illustrated in FIG. 3, it is obvious to those skilled in the art that the MBMS service is provided via the Node B. Also, a description will be made of an MBMS control message transmitted for the MBMS service.
Referring to FIG. 3, through an Announcement process in step 331, an SGSN 304 announces, to a particular UE 300, fundamental information on a particular MBMS service, for example, an MBMS service identifier (ID) and information on availability of the MBMS service, i.e., start time information and duration information of the MBMS service.
If it is determined through the MBMS service Announcement process that there is a desired MBMS service, the UE 300 performs a Joining process in step 341 to send an MBMS service request to the SGSN 304.
In the Joining process of step 341, the UE 300 transmits a Joining Request message to the SGSN 304. The Joining Request message includes an identification code for a particular MBMS service the UE 300 desires to receive in an MBMS service list transmitted by the SGSN 304, and an UE ID of the UE desiring the MBMS service. The SGSN 304 then performs authentication on the UE 300 that requested the MBMS service, and informs the UE 300 whether the MBMS service is available as a result of the authentication. Further, the SGSN 304 stores therein a list of UEs desiring to receive a particular MBMS service, and position information of the UEs.
Thereafter, if a message indicating a start of the MBMS service is received from a BM-SC, the SGSN 304 transmits in step 351 a Session Start message to an RNC 302 that controls a cell where the UE 300 is located.
In step 352, the RNC 302 informs the UE 300 of availability of the MBMS service through a Notification message. The RNC 302 assigns the Notification message to a common channel such as a secondary-common control physical channel (S-CCPCH) before transmission to the UE 300. The Notification message is transmitted over an MBMS control channel (MCCH) to inform the UE 300 that the SGSN 304 will start providing the MBMS service to the UE 300 that desires the MBMS service. The Notification message is paged by a plurality of UEs, and is used for performing a group paging process. The group paging process in step 352 is distinguishable from the individual paging process.
In step 361, the UE 300 transmits a Notification Response message to the SGSN 304 in response to the Notification message. The RNC 302 determines the number of UEs desiring to receive the MBMS service for each cell through the Notification Response message, and determines a type of a radio channel to a corresponding cell. If the number of UEs desiring to receive the MBMS service is larger than or equal to a predetermined threshold, the RNC 302 provides the MBMS service to the UEs over a common channel for point-to-multipoint (PtM) transmission. However, if the number of UEs desiring to receive the MBMS service is smaller than the predetermined threshold, the RNC 302 separately provides the MBMS service to each UE over a dedicated channel for point-to-point (PtP) transmission.
In step 371, the RNC 302 transmits information on a radio bearer (RB) for transmitting the MBMS service to the UE 300 over an MBMS control channel (MCCH). Based on the MBMS RB information, a radio bearer is set up between the RNC 302 and the UE 300. The RB setup process sends information on a radio channel for providing the MBMS service to related devices, so that the UE 300 can correctly restore the transmitted MBMS service using the MBMS RB information. The MBMS RB information includes radio channel information, for example, Orthogonal Variable Spreading Factor (OVSF) code information, transport format information, radio link control (RLC) information, packet data convergence control information, etc.
If a type of the MBMS channel is determined to be a PtP type, the MBMS RB information is transmitted to the UE 300 over a dedicated control channel. However, if a type of the MBMS channel is determined as a PtM type, the MBMS RB information is transmitted to UE 300 over the MCCH. The MCCH is a channel provided with control information related to the MBMS service, and exact characteristics of the MCCH is now under discussion. According to the discussion results made to date, the MCCH has the following characteristics:
1. MCCH is separately formed for each cell.
2. MCCH is transmitted over a common physical channel such as S-CCPCH.
3. UEs can acquire information on MCCH separately formed for each cell as system information.
In step 381, the RNC 302 transmits MBMS data provided from the SGSN 304 to the UE 300 over an MBMS RB, and the UE 300 receives the MBMS data transmitted over the MBMS RB.
FIG. 4 is a diagram illustrating a structure where a plurality of Frequency Allocations (FAs) overlap each other in a particular area. Referring to FIG. 4, an RNC has one or more FAs, and provides MBMS data through the FAs. Reference numerals 401, 402, 403 and 404 illustrated in FIG. 4 represent the same geographical area, and represent cells where MBMS services are provided using different FAs. One or more UEs located in the four FAs are provided with MBMS data transmitted from the FAs. That is, the FAs represent the same area in terms of geography, but represent 4 different service cells in terms of frequency at which the MBMS data is supported. As described above, conventionally, a plurality of FAs overlap each other in the same geographical area, and each of the FAs serves the same MBMS data to one or more UEs.
Here, the MBMS data to be transmitted is the same MBMS data, and radio resources are separately assigned to the FAs for transmission of the MBMS data, resulting in a waste of limited radio resources.
If the MBMS service is unavailable at a particular FA among the FAs, UEs included in the FA where the MBMS service is unavailable cannot receive the MBMS service. For example, if FA2 402 can support the MBMS service but FA1 401, FA3 403 and FA4 404 cannot support the MBMS service, then UEs included in FA1 401, FA3 403 and FA4 404 cannot receive the MBMS service.
Therefore, a method for providing the MBMS service to UEs included in an FA that cannot support the MBMS service is required.